1. Field of the Invention
The present invention relates to a dry running gas valve having a disk-shaped valve element with a number of throughflow channels, which valve element interacts sealingly with a valve seat, and wherein the valve element is connected to a magnet armature which interacts sealingly with an electromagnet arranged in the gas valve.
2. The Prior Art
Gas valves for feeding gaseous fuel into the combustion chamber of an internal combustion engine require large opening cross-sections in order to be able to introduce enough gaseous fuel into the cylinder chamber within the short opening times available. Such gas valves are often opened by electromagnets, wherein the electromagnet has to allow a sufficient stroke and provide a sufficient magnetic force in order to be able to feed the required gas quantities within the short opening times. In addition, opening and closing times as short as possible are desired so that the time during which the gas valve can be fully open during the crankshaft cycle is as long as possible. During one crankshaft cycle which, expressed in rotation angle of the crankshaft, takes 720° for a four-stroke engine and 360° for a two-stroke engine, gaseous fuel is fed once into the combustion chamber of the internal combustion engine. For this, usually, very short times are available so that the gas valve has to open and close rapidly and has to provide a sufficient flow cross-section in order to be able to introduce the needed gas quantity within the time available. Typically, for introducing the gaseous fuel into large engines, 90° crank angle of the entire crankshaft cycle is available. Within this injection time, the gas valve has to be opened, the gaseous fuel has to be fed into the combustion chamber, and the gas valve has to be closed again. Thus, depending on the speed, only a few milliseconds, typically 10-25 ms, are available. Accordingly, the gas valve has to be capable of switching rapidly and has to provide a large opening cross-section in order to be able to feed enough gaseous fuel within these short times. Specifically in case of large gas valves for large engines, these requirements are difficult to achieve.
For this reason, similar to compressor valves, gas valves often have a disk-shaped valve element with a plurality of throughflow channels, wherein the valve element interacts sealingly with a valve seat which has a plurality of throughflow channels as well. Such a valve element typically consists of a number of concentric rings which are connected to each other by radial webs distributed over the circumference. One difference between a gas valve and a compressor valve is that a compressor valve is self-actuating whereas a gas valve is controlled, e.g. by means of an electromagnet, thus, is actively switched. While the valve element of a compressor valve is stopped at the valve catcher and rests thereon over the full surface due to the applied pressure, the valve element of a gas valve has to be stopped at a limit stop. In a compressor valve, the center pin is designed with a diameter as small as possible so as to be able to keep the available flow area as large as possible. Since, in addition, the opening force, e.g. a magnetic force, acts on the valve element of a gas valve, bending stress can occur in the valve element when resting against the limit stop which can result in that the valve element bends significantly and, e.g., abuts against the electromagnet or the flow of the gas through the valve is affected. This is in particular the case if the opening force acts centrally on the valve element, e.g. in case of an embodiment having a central pin to which the valve element is fastened and the limit stop is arranged radially on the outside. Those components which are subjected to bending therefore have to be dimensioned stronger in an adequate manner which, in turn, means more mass and slower opening and closing times. Another possibility is to select the residual air gap large enough that the valve element, despite bending, does not abut against the electromagnet. However, a large air gap reduces the effective magnetic force which either reduces the switching differential pressures and the achievable opening speeds or requires larger electromagnets, which is undesired in both cases.
An example for such a gas valve is disclosed, e.g., in U.S. Pat. No. 5,398,724 A. The valve element of this gas valve is fastened to the magnet armature by means of a central pin. Over the entire circumference of the valve element, recesses for receiving spiral springs are provided. The other ends of the spiral springs are arranged in recesses at a spring seat which also forms the limit stop for the valve element. The springs, on the one hand, generate the closing force and, on the other, guide the valve element. Since the limit stop for the valve element is provided radially on the outside, undesired bending stress is generated in the valve element.
Normally, in a compressor there is always oil in the compressed medium (e.g. air) from the lubrication of the compressor, which is why the parts of a compressor valve are also lubricated at the same time. In such a “lubricated” compressor valve, the valve element can be guided on the central center pin. In contrast, in dry running compressors, thus in case of valves without such an inherent lubrication, the valve element can not be guided centrally on the center pin due to friction and the associated wear and temperature increase. Thus, only control-arm-guided, dry running compressor valves are known in which a part of the valve element is held stationarily and said stationary part is connected via so-called control arms to the movable part of the valve element which is guided in this manner with low friction.
Also in the case of gas valves, up to now, no dry running gas valves are known in which the valve element is guided in a guide. A guided valve element for a lubricated gas valve is known, e.g. from EP 425 327 B1 in which pressurized lubricant is fed to the valve. However, this gas valve does not have a disk-shaped valve element with a number of throughflow channels, but the valve element consists here of a circular magnet armature which is connected to a vertical piston. The piston's front side facing away from the magnet armature forms the sealing which interacts with an end face of a valve seat. The piston is guided radially outwardly in a cylindrical passage of the gas valve. Due to this arrangement, the problem of the deflection of the valve element does not occur here at all.
The aforementioned U.S. Pat. No. 5,398,724 A also shows a dry running gas valve in which the guidance of the valve element takes place via spiral springs and not via guide faces.
It is an object of the present invention to provide a dry running gas valve in which the problems with the deflection of the valve element are largely avoided and high opening speeds can still be achieved.